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BOOMERANG's 1998 Antarctic balloon flight scanned a low-dust region with a microwave telescope near $38\mathrm{km}$ and bolometers at $0.3\mathrm{K}$. Ground beam measurements and microwave angular dipole calibration connected signals to sky temperature. Frequency-map and time-split differences tested contamination. The 2000 paper fitted the Cosmic microwave background power spectrum, finding ${\ell }_{\mathrm{peak}}=197\pm 6$ at one standard deviation. Its near-flat-geometry inference used a chosen model family and parameter priors; secondary peaks were not yet established.^[ref]